This invention relates to a flame sensor for a burner and, more particularly, to a flame sensor in which pulsed signal amplification occurs at or near the sensor itself and further wherein the pulsed signal being sensed is monitored to ensure circuit integrity between the amplifier and a microcontroller which controls burner operation.
Flame sensors are used to sense the presence or absence of a flame in a heater or burner, for example, or other apparatus. The heater or burner may be used to heat water or ambient air and the fuel used may be one of several different types.
In the event the flame is extinguished, although not deliberately so, the sensor is adapted to sense the absence of the flame. The flame can be extinguished, for example, by fuel starvation or other malfunction. After sensing the extinguishing of the flame, the sensor or its related circuitry will send an alarm signal to a microcontroller. The microcontroller will take appropriate action such as shutting down the heater or burner by terminating fuel flow. In such a manner, serious safety problems such as continued fuel flow into a hot burner without a flame being present for combusting the fuel are avoided.
However, it is inconvenient to terminate the fuel flow if the flame is present and the burner is working properly. The termination of the fuel flow causes termination of the operation of the burner or heater unintendedly if the flame sensor sends an incorrect signal to the control panel. The present invention has as an object the avoidance of inadvertent burner shutdown and, as well, the avoidance of burner operation when the flame is extinguished.
One reason for unintended burner shutdown is signal contamination of the signal from the flame sensor, Since the power of the signal previously sent to the amplifier is quite small, in the range of 50 mv to 200 mv, and since the amplifier was located some distance from the sensor, any noise caused by common mode radiation or other RF signals could disrupt the integrity of the signal being passed to the amplifier by the sensor. This causes incorrect information to be read by the microcontroller with the result that the heater could be inadvertently shut down or, alternatively, the heater may continue to run in a flame out condition. Both scenarios are not desirable.
A further problem with the prior art is to determine where the malfunction in the burner may occur. A number of problems may occur which will shutdown the burner or otherwise cause malfunctions. Troubleshooting such malfunction can be time consuming, inefficient and costly.
According to one aspect of the invention, there is provided a flame monitor for sensing the presence of flame in a burner, said flame monitor comprising a sensor located adjacent said flame to sense the variation in radiation emanating from said flame and to produce a first signal, an amplifier to amplify said signal being received from said sensor and to pass said amplified signal to a microcontroller located remotely from said amplifier and said sensor, said microcontroller being operable to terminate operation of said burner upon receiving a predetermined change in said signal being received from said amplifier.
According to a further aspect of the invention, there is provided a method for sensing the presence of flame in a burner and for terminating operation of said burner when said flame is not present comprising the steps of sensing the presence of radiation from said flame with a sensor located relatively closely to said flame and sending a signal from said sensor to an amplifier when said radiation is sensed, said signal being amplified by said amplifier with relatively little change occurring in said signal between said sensor and said amplifier and forwarding said amplified signal to a microcontroller located remotely from said sensor and said amplifier.
According to a further aspect of the invention, there is provided apparatus for monitoring connection integrity between an amplifier and a microcontroller, said connection comprising positive, ground and signal connectors, a missing pulses detector operable to determine the presence or absence of pulses in said connection and a sensor supervisor to monitor the transition of voltage from a high to a low or a low to a high condition, either of said missing pulses detector or said sensor supervisor sending an alarm condition signal to said microcontroller if said missing pulses detector detects missing pulses or if said sensor does not sense voltage transition.
According to yet a further aspect of the invention, there is provided a method of monitoring connection integrity between an amplifier used to amplify the signal received from a sensor and a microcontroller, said method comprising generating a series of pulses in a signal connection, monitoring said pulses with a missing pulses detector and generating an alarm signal when said missing pulses detector detects missing pulses in said signal connection.
According to still yet a further aspect of the invention, there is provided a method of monitoring connection integrity between an amplifier used to amplify the signal received from a sensor and a microcontroller, said connections comprising a positive and a ground connection extending between said amplifier and said microcontroller, said method comprising monitoring the positive and ground connections with a sensor supervisor, said sensor supervisor transitioning from a high to a low or a low to a high voltage condition if one of said positive or ground connections are interrupted and said sensor supervisor generating an alarm signal to said microcontroller if said voltage transitions from said high to said low or said low to said high condition.